Asymmetrically foamable strand

ABSTRACT

GENERALLY LINEAR FOAMABLE STRANDULAR PARTICLES WHICH ARE ASYMMETRICAL ABOUT A PLANE GENERALLY CONTAINING THE LONGITUDINAL AXIS PROVIDE A DESIRED CURLED DUNNAGE MATERIAL WHEN HEATED TO CAUSE FOAMING. A WIDE VARIETY OF METHODS MAY BE USED TO INTRODUCE THE DESIRED ASYMMETRY.

l March 27, 1973 R. E. sKocHDoPoLE ETAL 3,723,240

ASYMMETRICALLY FOAMABLE STRAND Filed May 27, 196s Z9 y .2f {25.5 6

INVENTORS.

BY Maw.

GE/V

United States Patent O W U.S. Cl. 161--173 3 Claims ABSTRACT F THEDISCLOSURE Generally linear foamable strandular-particles which areasymmetrical about a plane generally containing the longitudinal axisprovide a desired curled dunnage material when heated to cause foaming.A Wide variety of methods may be used to introduce the desiredasymmetry.

This invention relates to an improved dunnage-producing material.

Foamed plastic particles or Strands are known to be highly desirable forpackaging articles for protection in shipping by absorption of shock andisolation of the article from the Walls of the shipping container.Typical materials are set forth in U.S. Letters Patent 3,066,382;3,188,264 and 3,251,728. Short hollow cylinders of foam plastic are alsoemployed as a dunnage or packing material. Although such packingmaterials are highly desirable, they sufer from a substantial andsignificant problem and that is the high cost of shipping expandedparticles due to their very low bulk density. It is, therefore, verydesirable to ship a product having a maximum bulk density andsubsequently expanded at the point of use into the desired form. Twogeneral types of foamed particulate plastic packing are employed. One istypied by the particles of U.S. Pat. 3,188,264 which is a pourablepacking; that is, it flows readily. The other variety of packing isdepicted in U.S. Pats. 3,066,382 and 3,251,728. Such packing generallyis not free-flowing and has a very strong tendency to interlock byvirtue of the fact that the strands have a curled and twistedconfiguration. In general, a foamable strand or particle on foaming willassume a coniiguration which is not an exact replica of the unfoamedconfiguration, but generally the foamed con- -guration will be similarto the unfoamed conguration. Thus, if a cylindrical strand is foamed,minor distortion from a cylindrical configuration occurs. Frequently,such distortion is relatively minor and is insufiicient to providebulking and curling of the strand into a configuration desirable forpacking. For example, short helical segments of from one to four or fiveturns are often desirable as such a configuration provides a dunnagematerial or minimal bulk density and a reasonable degree of interlockingunder pressure. Such particles are quite unsatisfactory to ship inquantity and the unfoamed precursor of such a strand or particle alsohas a relatively low bulk density and is similarly undesirable.

It would be beneficial if there were available an improved generallylinear expandable synthetic resinous particle which, on heating to afoaming temperature, would curl to form a generally helicalconfiguration.

These beneits and other advantages in accordance with the presentinvention are achieved in an article which is prepared by providing aheat plastiied mass of a synthetic resinous material containing anexpanding agent, the heat plastiiied mass being capable of expansion toform a plurality of closed gas-filled cells, maintaining the heatplastiiied foamable material under pressure, subsequently cooling theheat plastied mass, forming the mass into a plurality of elongatestrands, discharging the strands from a shaping configuration withoutsignificant foaming occurring in the strands, subsequently severing$123,245@ Patented Mar. 27, i973 ICC the strands to form a plurality ofelongate elements 0f relatively high bulk density, subsequently heatingthe elongate elements or strand portions to an elevated temperatureSutiicient to cause them to expand and form a plurality of gas-filledcells therein, the improvement which comprises introducing radialasymmetrical foamability into the strandular material prior to foamingto hereby cause curling to a desired degree upon foaming.

Strands or particles in accordance with the present invention arereadily prepared from a wide variety of synthetic resinous materialsincluding polymers which comprise, in chemically combined form, at leastabout 70 percent by weight of at least one alkenyl aromatic compoundhaving `the general formula wherein Ar represents an aromatichydrocarbon or a nuclear halohydrocarbon radical of the benzene series,and R is hydrogen or the methyl radical. Examples 0f such alkenylaromatic polymers are homopolymers of styrene, a-methyl styrene, o-, m,and p-methylstyrene, ar-ethylstyrene, tertiary butylstyrene andar-chloro-styrene; the copolymers of two or more of such alkenylaromatic compounds with one another; and copolymers of one or more ofsuch alkenyl aromatic compounds with minor amounts of other readilypolymerizable olenic compounds such as divinylbenzene,methylmethacrylate, or acrylonitrile, etc. Also suitable are aliphaticolefin polymers which are normally solid polymers obtained bypolymerizing at least one u-monoolenic aliphatic hydrocarbon containingfrom 2 to 8 carbon atoms, such as ethylene, propylene, butene-l,pentene-l, 3-methylbutene- 1, 4-methylpentene-1, 4-methylhexene-l, or5methyl hexene-l, alone, with one another, or with various otherpolymerizable compounds, but the polymers of ethylene or propylene aloneare preferred because they produce tough resilient and tine-celledchemically inert products.

Examples of suitable polymerizable organic compounds which can bepolymerized with ethylene or propylene are vinyl acetate, C1-C4 alkylacrylates, such as ethyl acrylate, styrene, lower alkyl esters ofmethacrylic acid, such as methyl methacrylate, tetraliiuoroethylene andacrylonitrile. Copolymers containing in chemically combined form apredominant amount, eg., percent by weight or more, of ethylene orpropylene with not more than 25 percent of one or more of such otherpolymerizable compounds can be used. The aliphatic olen polymers can bemodied by blending with polymeric materials, e.g., polyisobutylene,acrylonitrile-butadiene rubbers, poly- (2-chlorobutadiene-1,3),polyisoprene, or ethylene-vinylacetate copolymers. Halogenated aliphaticolefin polymers can also be used, as well as polymers of a Wide varietyof ethylenically unsaturated monomers which produce lfoamablethermoplastic compositions including polymers of isopropenyl toluene,vinyl naphthalene, and the esters of at-methylene aliphaticmonocarboxylic acids, such as methyl acrylate, ethyl acrylate, n-butylacrylate, isobutyl acrylate, dodecyl acrylate, 2-chloroethyl acrylate,2chlo ropropyl acrylate, 2,2dichloroisopropyl acrylate, phenyl acrylate,cyclohexyl acrylate, methyl a-chloroacrylate, methyl methacrylate, ethylmethacrylate, methyl ethacrylate, acrylonitrile, methacrylonitrile;vinyl esters, such as vinyl acetate, vinyl chloroacetate, vinylpropionate, vinyl butyrate, vinyl laurate, vinyl stearate, vinyl etherssuch as vinyl methyl ether, vinyl isobutyl ether, vinyl 2-chloroethylether; vinyl ketones, such as vinyl methyl ketone, vinyl hexyl ketone,methyl isopropenyl ketone, isobutylene, vinylidene halides, such asvinylidene chloride, vinylidene chlorofluoride, N-vinyl compounds suchas N-vinyl pyrrole, N-vinyl carbazole, N-vinyl indole, N- vinylsuccinimide, acrolein, methacrolein, acrylamide,

methacrylamide, N-methylol acrylamide; and allyl compounds such as allylalcohol, methallyl alcohol, allyl acetate, allyl methacrylate, allyllactate, allyl a-hydroxy-isobutyrate, allyl trichlorosilane, allylacrylate, methallyl phosphate, and the like.

Foamable compositions of polymers are well known in the art and areprepared by incorporating therein a gas, volatile liquid or combinationsof gas, volatile liquid or solid gas releasing blowing agents whichcause expansion ofthe polymeric material on heating. It is well known inthe art to extrude foamable particles by cooling the viscous melt belowthe blowing temperature under pressure, subsequently passing the strandinto atmospheric pressure and rapidly cooling the strand to a solid ornonheat plastified state.

It is essential and critical to the present invention that at theexpanding temperature asymmetry exist in the particle or strand portionto be expanded; that is, one side of the particle should expand to alesser degree, if at all, than the other. The degree of asymmetrycontrols the tendency of the particle to twist and curl and form agenerally non-linear configuration. Such asymmetry may be introducedinto a foamable resinous material in a number of ways. For example, agenerally linear strand of synthetic resin can be scraped to remove afew percent of its cross-sectional area; for example, about percent, andwhen subjecting it to foaming conditions on expansion, the strand curls.Depending on the particular scraping pattern, a wide variety of coiledshapes are obtained. Another method of introducing asymmetry into thestrand is by subjecting one side of the strand to heat sufficient todeform the strand without introducing significant foaming or slightfoaming and subsequently foaming the remainder of the strand orparticle. Oftentimes the region which has been previously heat treatedwill foam to a greater extent than the non-heat treated portion if theheating has been sufficient merely to soften a portion of the strand.Prolonged heating or repeated heating of one side of a foamed strand orparticle sometimes will introduce curling in the opposite directionwherein the treated portion lies on the inside of the curve of theparticle, presumably because removal or deactivation of a portion of theblowing agent results in non-uniform distribution. Localizedplasticization also causes disymmetry. Exposure of one side of afoamable strand to a plasticizer or fugitive plasticizer will alsoresult in curling. Particularly acceptable are solvents or swellingagents applied in a relatively small quantity to one side of theparticle or strand. Asymmetry is also introduced into strands byincluding as a minor portion of the strand an element which isnon-foaming or relatively low foaming. Such strands can be prepared byuse of a wire coating crosshead die wherein a strandular element such asa cotton thread is coated with the expandable material and the threadpositioned within the strand and adjacent one edge thereof rather thancentrally disposed as is normally done with wire coating on extrusion.

The well known process of simultaneous extrusion may be used wherein astrand is extruded; a major portion of the strand is expandable and aminor portion of the strand exposed along one side thereof is relativelynon-expandable. By the term simultaneous extrusion is meant thesimultaneousl extrusion of polymers, having different physicalcharacteristics, through a single orifice to provide a unitary article.

Asymmetry is also introduced to the strand by coating one side or aportion of a side of the strand with a second material that has aperipheral modulus at a higher temperature. This is readily accomplishedby solution or melt coating or by lamination of either a non-expandingor poorly expanding material. For example, the coating of one side of astrand with a lacquer which does not contain a blowing agent or containsrelatively little blowing agent and has a different modulus at theexpansion temperature of the strand is sufiicient to cause curling whenthe strand is heated.

When foamable compositions containing volatile or fugacious liquids asexpanding agents are utilized, foaming asymmetry is readily introducedby selecting the proper die geometry for extrusion. Thus, if a dieorifice is utilized which introduces substantial asymmetry such as byproviding a narrow ridge adjacent one edge of the strand, the volatilefoaming agent will tend to diffuse from the ridge rnore rapidly thanfrom the main body of the strand, and therefore when foamed, expand lessand cause the strand to curl and twist.

Regardless of how foaming asymmetry is introduced into the strand, manydierent foamed shapes are obtained depending upon the position of theasymmetry. If a non-foaming or low foaming region is introduced into astrand which is uniform in nature and extends along one side thereoffrom end to end, the usual tendency is to foam to a helical shape. Ifsuch a strand is twisted or the foaming asymmetry disposed in more orless of a helical manner about its outer surface, a wide variety ofcurled shapes are obtained, depending on the degree of foamingasymmetry, the relative length of the strand portion being foamed andthe like. By intermittently or periodically reducing foaming asymmetry,foamed strands having a number of bent and straight sections willresult, the simplest form of such a strand being a foamable strandhaving a length of three units and having foaming asymmetry introducedover a longitudinal distance of 1A to l/2 unit of length in the centerof the strand. On foaming, the strand will have a generally centrallydisposed bend and relatively straight leg or end portions. Byintroducing foaming asymmetry wherever a bend is desired, square shapessuch as square Us, squares, rectangles and the like are obtained if theasymmetry is introduced along one side of the strand. However, ifselective asymmetry is introduced to a strand in such a way that theasymmetry does not lie in a single plane containing the longitudinalaxis of the strand, three dimensional bending occurs on foaming; thatis, when foamed, portions of the strand adjacent each bend are generallycoplanar and each of the portions of adjacent bends may lie in planeswhich are angularly disposed relative to any other plane containing apair of strand portions. TheI method of the invention therefore permitsthe foaming of a relatively straight strand into almost any desiredconfiguration.

Further features and advantages of the present invention will becomemore apparent from the following specilication taken in connection withthe drawing wherein:

FIG. 1 depicts a view of a generally linear elongate strand inaccordance with the present invention.

FIGS. 2, 3 and 4 depict views of a curled strand.

FIGS. 5, 6 and 7 depict schematic cross-sectional configurations ofasymmetric strands in accordance with the invention.

In FIG. 1 there is schematically depicted a strand generally designatedby the reference numeral 10 having a first end 11 and a second end 12, afirst side 13 and a second side 14. The sides 13 and 14 differ inmodulus. The strand is composed of expandable synthetic resinousthermoplastic material.

FIG. 2 depicts a foamed strand 10a which forms a generally spiralpattern and results from the expansion under heat of a strand such asthe strand 10 of FIG. 1.

FIG. 3 depicts a foamed strand 10b having a generally helicalconfiguration.

FIG. 4 depicts a foamed strand having a generally spiral helicalconfiguration.

FIG. 5 depicts a sectional view of a strand 20 having a first side 21and a second side 22, the sides 21 and 22 being generally diametricallyopposed. The strand 20 has a major portion 23 of readily foamablethermoplastic material and a second or minor portion of a high modulusor non-foamable material extending side 22. j f v FIG. 6 depicts across-sectional view of a strand 25 having a first side 26 and a secondside 27 and a major portion 28 of av readily foamable synthetic resinousmaterial, the sides 26 and 27 being generally diametrically opposed. Anon-expandable elongate material 29 is encapsulated within the strand 25and extends along the second side 27. The material 29 beneficially is ofa synthetic resinous thermoplastic nature or a non-thermoplastic naturesuch as a textile liber as hereinbefore described.

FIG. 7 depicts a sectional view orf a strand 30. The strand 30 comprisesa generally cylindrical foamable portion 31, having a first side 32 anda second side 33, the sides 32 and 33 being generally diametricallyopposed. Disposed on the side 33 is a layer of a non-expandable material34 generally conforming to the external surface of the portion 31. v

The invention is further illustrated but not limited by the followingexamples:

EXAMPLE 1 A plurality of foamable generally linear polystyrene strandsareprepared employing the procedure set forth in U.S. Pat. 3,066,382.The strands are cut to provide a plurality of portions about 5.6centimeters in length and 2.5 millimeters in diameter. A lacquer isprepared by dissolving a polymer of 85 Weight percent yinylidenechloride and l5 weight percent acrylonitrile in nitromethane to providea lacquer containing 15 weight percent solids. A number of strands arecoated on one side with the lacquer generally in the manner depicted inFIG. 5 and the lacquer allowed to dry overnight. A number of the coatedstrandsl and uncoated strands are heated by exposing to steam under lpounds of pressure per square inch gauge for about 30 seconds. Thecoated strands expand to a diameter of about 7 millimeters and form agenerally U-shaped particle having an outside length of about 9.5centimeters and an inside length of about 6.4 centimeters. The uncoatedparticles expand to form generally linear pieces about 7 millimeters indiameter and having a length of about 9.3 centimeters.

EXAMPLE '2 Portions of foa-mable polystyrene strands of Example l areadhered to a -mi1 thick polyester lilm employing the vinylidene chloridelacquer utilized in Example l. The strand portions are coated on oneside with lacquer and placed on the polyester iilm. When the lacquer isdry, portions of the polyester iilm which are not adhered to the strandare trimmed away to provide a configuration generally similar to thatshown in FIG. 7 wherein the polyester -iilm has a width of about 5millimeters. Exposure of the composite strand to steam at pounds persquare inch gauge for 30 seconds provides a foamed coiled strand ofabout lil/2 turns in a generally helical coniguration.

EXAMPLE '3 'Polydichlorostyrene which becomes Huid at about 225 C. isheated on a hot bar until it becomes molten. A strand of expandablepolystyrene of AExample 1 is rapidly drawn across the molten surface ofthe polydichlorostyrene to provide a thin coating of thepolydichlorostyrene adhered to one side of the strand. LExposure of thepolydichlorostyrene-coated strand to steam at l0 pounds per square inchgauge for 30 seconds results in the formation of a loop. j

along the second EXAM PLE 4 A portion of the foamable uncoated strandsof Example l are scraped with the sharp edge of a knife to remove about5 percent of the original cross-sectional area of the strand. Thestrands are exposed to steam at 10 pounds per square inch gauge for aperiod of one minute, the strands bent and curled at the locations wherethe strands are scraped. The scraped side of the strand lies on theoutside of the foamed strand and the curvature becomes greater as theamount of material removed by scraping increases. Depending on thescraping pattern, that is, the material removed from the strand, gentlecurves, helices, pretzel strands, tightly coiled balls are obtained onfoaming.

EXAMPLE 5 An untreated polystyrene strand of Example l is passed acrossthe surface of a metal bar which is heated to about 175 C. The surfaceof the strand is tattened Where it has been in contact with the heatedsurface. The strand is subsequently exposed to steam at a pressure of l0pounds per square inch gauge for a period of one minute; the strandfoams and curls.

lEXAMPLE 6` An untreated polystyrene strand as employed in 'Example l iscoated with Xylene to wet one side of the strand. The strand is thentreated with steam at a pressure of l0 pounds per square inch gauge fora period of one minute. A tightly curled foam strand is obtained.

EXAMPLE 7 A foamable strand is prepared by the extrusion of a heatplastiiied foamable polystyrene mixture containing about 5 weightpercent pentane as an expanding agent. A polymer of 25 weight percentacrylonitrile and 75 weight percent styrene is simultaneously extrudedto provide a composite strand which is about 95 weight percentexpandable polystyrene and about 5 weight percent polyvinyl chloride.The polyvinyl chloride is disposed adjacent one edge of the strandgenerally in the manner depicted in FIG. 6. The strand is severed intolengths of about l0 centimeters and subjected to steam at about 10pounds per square inch gauge for about one minute. A tightly coiledgenerally helical configuration is obtained.

EXAMPLE 8 Expandable strands of Example 1 are wet with benzene on oneside thereof at a location about midway between the ends and exposed tosteam at a pressure of l0 pounds per square inch gauge for 30 seconds topr0- vide a plurality of foamed strands having a centrally disposed bendof about 60. Repetition of the foregoing procedure wherein alongitudinal central side portion of a strand Wet with xylene instead ofbenzene provides a plurality of strands having centrally disposed bendsof from about I to l120". When the strands are wet with xylene atlocations about 1.5 centimeters from their ends, a lU-shapedconfiguration results. By wetting a strand with xylene at a locationabout 2 centimeters from each end, each dampened support being radiallydisplaced about a strand is obtained having two bends of about 90 andthe terminal leg portions are displaced about 90 from being coplanar.

EXAMPLE 9 A plurality of foamable generally linear polystyrene strandsare prepared employing the procedure as generally set forth in U.S. Pat.3,066,382 employing normal pentane as a blowing agent. The strands areextruded from a die having a plurality of generally circular openingshaving a diameter of about 0.142 inch. A V-shaped notch is formed in oneside of the die openings and the notch has a depth of about 0.022 inchand a width of about 0.015 inch at its point of contact with a projectedcircle of the die opening. The extruded strands have a small narrowridge along one side thereof. The strands when cut to a length of about6 centimeters and exposed to steam under 10 pounds of pressure persquare inch for about one minute, foam to provide a plurality of curledstrands. Twisting of the strand on emergence from the die and subsequentfoaming results in highly convoluted foamed strands.

In a manner similar to the foregoing illustrations, other foamablesynthetic resinous compositions are readily formed into curled foamedstrands.

As is apparent from the foregoing specification, the present inventionis susceptible of being embodied with various alterations andmodifications which may differ particularly from those that have beendescribed in the preceding specification and description. For thisreason, it is to be fully understood that all of the foregoing isintended to be merely illustrative and is not to be construed orinterpreted as being restrictive or otherwise limiting of the presentinvention.

What is claimed is:

1. A generally linear elongate strand of a foamable synthetic resinousmaterial, the synthetic resinous material being capable of forming aplurality of closed gaslled cells on heating, the elongate strandhaving:

a first end and a second end and a longitudinal axis,

a first side and a second side, the first and second sides beinggenerally diametrically opposed, the second side having a plasticizerdisposed therein, the foamability of the first side and second sidebeing asymmetric with respect to the longitudinal axis, whereby thestrand on heating to a foaming temperature curls to form a curvedconfiguration.

2. A plurality of generally linear elongate strands of a foamablesynthetic resinous material being capable of forming a plurality ofclosed, gas-filled cells, the elongate strands having:

a first end and a second end and a longitudinal axis,

8 a first side and a second side, the first and second sides beinggenerally diametrically opposed, a minor portion of a non-foamablematerial disposed within the strands and being adjacent 'the second sidewhereby the foamability of the first and second sides are asymmetricwith regard to the longitudinal axis and the strands on heating to afoaming temperature curl to form a substantially similar curvedconfiguration. 3. A plurality of generally linear elongate strands of aYfoamable synthetic resinous material being capable of forming aplurality of closed, gas-filled cells, the elongate strands having:

a first end and a second end and a longitudinal axis, a first side and asecond side, the first and second sides being generally diametricallyopposed, a minor portion of a non-foamable material disposed thereon andbeing adjacent the second side whereby the foamability of the first andsecond sides are asymmetric with regard to the longitudinal axis and thestrands on heating to a foaming temperature curl to form a substantiallysimilar curved configuration.

References Cited UNITED STATES PATENTS 3,066,382 12/1962 zweigle et a1161-173 X ROBERT F. BURNETI, Primary Examiner R. A. DAWSON, AssistantExaminer 30 Us. C1. x.R.

l61-175, 176, 177, 178, 179; 206-46 FC; 260-2.5 H, 2.5 HA, 2.5 HB

